Growth of plural sample rods to determine impurity build-up during production of single crystal silicon ingots

Abstract

Methods for forming single crystal silicon ingots in which plural sample rods are grown from the melt are disclosed. A parameter related to the impurity concentration of the melt or ingot is measured. In some embodiments, the sample rods each have a diameter less than the diameter of the product ingot.

What is claimed is: 
     
       1. A method for producing a single crystal silicon ingot from a silicon melt held within a crucible comprising:
 heating polycrystalline silicon in the crucible to cause a first silicon melt to form in the crucible; 
 pulling a first sample rod from the first melt, the first sample rod having a first sample rod diameter; 
 measuring a first sample rod parameter related to the quality of the first sample rod and/or the first melt; 
 pulling a second sample rod from the melt, the second sample rod haying a second sample rod diameter; 
 measuring a second sample rod parameter related to the quality of the second sample rod and/or the first melt; 
 pulling a first product ingot from the first melt, the first product ingot having a diameter, the first sample rod diameter and the second sample rod diameter being less than the diameter of the first product ingot; 
 heating polycrystalline silicon in the crucible to cause a second silicon melt to form in the crucible; and 
 pulling a second product ingot from the second melt, the second product ingot having a diameter, the first sample rod diameter and the second sample rod diameter being less than the diameter of the second product ingot, wherein a growth condition of the second product ingot grown from the second melt is altered based at least in part on a rate of change in a difference between the measured first sample rod parameter and the measured second sample rod parameter. 
 
     
     
       2. The method as set forth in  claim 1  wherein the growth condition is selected from the group consisting of a hot-zone configuration, side heater power, heater geometry, crucible liner thickness, dopant concentration, impurity and dopant evaporation, gas flow rate, and chamber pressure. 
     
     
       3. The method as set forth in  claim 1  wherein the first sample rod parameter and the second sample rod parameter are the resistivity of the sample rod, the first sample rod resistivity and the second sample rod resistivity being measured by contacting the rod with a resistivity probe. 
     
     
       4. The method as set forth in  claim 3  further comprising:
 forming a planar segment on the first sample rod, the resistivity of the first sample rod being measured on the planar segment; and 
 forming a planar segment on the second sample rod, the resistivity of the second sample rod being measured on the planar segment. 
 
     
     
       5. The method as set forth in  claim 3  further comprising applying a current to each sample rod to measure a resistance of the sample rod. 
     
     
       6. The method as set forth in  claim 3  wherein each sample rod is secured by a measurement apparatus comprising a clamp that holds the sample rod while contacting the sample rod with the resistivity probe. 
     
     
       7. The method as set forth in  claim 3  further comprising annealing each sample rod in a thermal donor kill cycle prior to measuring a resistivity of the sample rod. 
     
     
       8. The method as set forth in  claim 1  wherein the diameters of the first and second sample rods are each less than 0.50 times the diameter of the first product ingot and the diameters of the first and second sample rods are each less than 0.50 times the diameter of the second product ingot. 
     
     
       9. The method as set forth in  claim 1  wherein the first and second sample rod and the first and second product ingot each has a resistivity of at least 1,500 Ω-cm. 
     
     
       10. The method as set forth in  claim 1  wherein polycrystalline silicon is not added to the crucible after the first sample rod is grown and before growth of the second sample rod. 
     
     
       11. The method as set forth in  claim 1  wherein the first sample rod parameter and the second sample rod parameter are the same parameter. 
     
     
       12. The method as set forth in  claim 1  wherein the first sample rod parameter and the second sample rod parameter is related to the impurity concentration of the melt, the first product ingot or the second product ingot. 
     
     
       13. The method as set forth in  claim 12  wherein the parameter is selected from the group consisting of the phosphorous concentration, boron concentration, aluminum concentration, gallium concentration, arsenic concentration, indium concentration, antimony concentration, total impurity concentration, dopant concentration, and resistivity of the sample rod. 
     
     
       14. The method as set forth in  claim 1  wherein the impurity concentration of the first rod and second rod are measured, the concentration of impurities in the first and second rods being less than 1×10 12  atoms/cm 3 , the impurity concentration being measured by Fourier-transform infrared spectroscopy or by photoluminescence. 
     
     
       15. The method as set forth in  claim 1  further comprising altering a growth condition of the first product ingot based at least in part on the measured first sample rod parameter and/or the measured second sample rod parameter.